The stormwater management plan shall be prepared using the general performance and technical standards requirements for plan format contained in Part 1, the Subdivision and Land Development Ordinance, and in this article with the following additions:
A.
Watershed location map: Provide a key map showing the location of
the development site within the watershed(s) and watershed(s) subareas(s).
On all site drawings, show the boundaries of the watershed(s) and
subarea(s) as they are located on the development site and identify
watershed name(s) and subarea number(s). Example: Use a USGS map with
the watershed, watershed subareas, and the subject property all outlined
and designated.
B.
Subwatershed map: A plan must be submitted showing all the drainage
areas and subwatersheds for the pre- and post-development peak runoff
calculations. Example: Use the site plan and draw the watersheds and
subwatersheds on the plan.
C.
Floodplain boundaries: Identify one-hundred-year floodplain on the
development site as shown on the FEMA mapping where applicable. In
the case where no FEMA mapping exists for a watercourse that boarders
the proposed development site, the applicant's determination
of the one-hundred-year floodplain for any watercourse or water body
on the development site shall be used.
D.
Natural features: Show all bodies of water (natural and artificial),
watercourses (permanent and intermittent), swales, wetlands and other
natural drainage courses on the development site, or which will be
affected by runoff from the development.
E.
Soils: Provide a map showing soil types and boundaries within the
development site (consult county, SCS, U.S. Geologic Survey for information).
The soils must be defined on the plan.
F.
Contours: Show existing and final contours at intervals of two feet;
in areas with slopes greater than 15%, five-foot contour intervals
may be used.
G.
Stormwater management controls: Show any existing stormwater management
and/or drainage structures, such as storm sewers, swales, culverts,
etc., which are located on the development site, or which are located
off site but will be affected by runoff from the development.
H.
Wetlands: Show any areas on the plan which have soils with hydric
inclusions, are shown on the National Wetlands Inventory Map and/or
support common wetland plants. These areas must be delineated by a
registered professional engineer who specializes in this field.
I.
Appendix A.[1] The preliminary stormwater management plan checklist must
be completed and submitted.
[1]
Editor's Note: Appendix A is included at the end of this chapter.
J.
K.
Land cover: Show existing and final land cover classifications as
necessary to support and illustrate the runoff calculations performed.
L.
Drainage area delineations: Show the boundaries of the drainage areas
employed in the runoff calculations performed.
M.
Stormwater management controls: Show any existing stormwater management
or drainage controls and/or structures, such as sanitary and storm
sewers, swales, culverts, etc., which are located on the development
site, or which are located off site but will be affected by runoff
from the development.
N.
DEP has regulations that require municipalities to ensure design,
implementation and maintenance of best management practices (BMPs)
that control runoff from new development and redevelopment after regulated
earth disturbance activities are complete. These requirements include
the need to implement post-construction with assurance of long-term
operations and maintenance of those BMPs.
Stormwater management facilities shall be constructed in accordance
with the following minimum specifications:
A.
All workmanship and materials shall conform to the borough construction
standards. In addition, all workmanship and materials shall conform
to the latest edition of PennDOT Form 408 and be supplied by manufacturers
or suppliers listed in PennDOT's Bulletin 15.
B.
All connections to existing storm sewer pipes shall be made by construction
of a suitable junction box (inlet or manhole) to provide access for
clean-out. No blind connections shall be permitted.
C.
All pipe outlets shall discharge onto a stone riprap blanket to prevent
erosion of soil. Riprap shall be sized considering pipe exit velocities
plus a factor of safety of 1.5.
D.
The discharge of stormwater runoff shall be to a well-defined drainage
course which has a defined bed and bank. If stormwater runoff cannot
be discharged to a defined drainage course, documentation of written
recorded drainage easement permission from each downstream property
owner shall be provided for all properties between the source of discharge
and the defined drainage course.
The stormwater management plan (including all calculations)
must be prepared, signed and sealed by a registered professional engineer,
or land surveyor with training and expertise in hydrology and hydraulics,
or such other professional persons as are qualified to make certification
under the laws of Pennsylvania. The preparer of the stormwater management
plan must fill out and submit Appendix C[1] with said plan.
[1]
Editor's Note: Appendix C is included at the end of of
this chapter.
A.
Runoff calculations are the acceptable methods of calculation for
use in determining the stormwater runoff correspondence with recommendations
of the Monongahela River Watershed Plan, prepared by the county, in
order to maintain a uniform, watershed wide approach. The following
methods for calculating pre- and post-development runoff rates have
been stipulated in the standards and criteria of the watershed plan:
(1)
Methods of runoff calculations, such as:
B.
All pertinent information used to generate the pre- and post-developed
discharge rates must be included with the stormwater management plan.
Also, the calculations for the sizing of the stormwater control facilities
must be submitted with the stormwater management plan.
A.
All inflow hydrographs to detention facilities must be routed using
methodology that analyzes detention storage and outflow simultaneously
with respect to time. The modified-puls method or approved equal,
as found in Haested Method's Pond 2 or the Army Corps of Engineers
HEC-1, is recommended.
B.
The following provisions shall be considered the overriding performance
standards against which all proposed stormwater control measures shall
be evaluated, and they shall apply to all areas of the borough.
C.
Stormwater shall not be permitted, as a result of development undertaken
after adoption of this Part 2 to collect upon any property, or to
pass from one property to another in a concentrated flow without benefit
of a legal easement, or to cross a public street on the surface.
D.
Any landowner and any person engaged in the alteration or development
of land which may affect stormwater runoff characteristics shall implement
such measures as are reasonably necessary to prevent injury to health,
safety or other property. Such measures shall include such actions
as are required:
(1)
To assure that the maximum rate of stormwater runoff is no greater
after development than prior to development activities; and
(2)
To manage the quality, velocity and direction of resulting stormwater
runoff in a manner which will not adversely impact the health on,
or value of, any affected properties.
E.
In the case of a development in which the total of the building and
paved surfaces on the site exceed 10,000 square feet, the developer
shall provide as part of the design a stormwater management narrative
signed and sealed by an engineer licensed in the Commonwealth of Pennsylvania.
The stormwater management narrative shall include an analysis of both
pre- and post-developed runoff conditions.
(1)
For the analysis of redevelopment projects 20% of the existing impervious
surface shall be considered meadow in good condition.
(2)
Post-development runoff rates after development shall not exceed
the pre-developed runoff rates including the reduction in impervious
surface required for redevelopment projects.
All proposed stormwater runoff control measures must be shown
on the plan, including methods for collecting, conveying and storing
stormwater runoff on site which are to be used both during and after
construction. Erosion and sedimentation controls must be shown on
a separate plan. The preliminary plan should provide information on
the general type, location, sizing, etc., of all proposed facilities
and their relationship to the existing watershed drainage system.
A.
If the development is to be constructed in stages, the applicant
must demonstrate that stormwater facilities will be installed to manage
stormwater runoff safely during each stage of development.
B.
A schedule for the installation of all temporary and permanent stormwater
control measures and devices shall be submitted.
All existing and proposed easements and rights-of-way for drainage
and/or access to stormwater control facilities shall be shown and
the proposed owner identified. Show any areas subject to special deed
restrictions relative to or affecting stormwater management on the
development site.
A.
Stormwater management easements are required for all areas used for
off site stormwater control, unless a waiver is granted by the municipality.
B.
Stormwater management easements shall be provided by the property
owner if necessary for access for inspections and maintenance, or
preservation of stormwater runoff conveyance, infiltration, and detention
areas and other BMPs, by persons other than the property owner. The
purpose of the easement shall be specified in any agreement under
Section 405.
C.
If a conservation easement is provided, the long-term ownership,
access, maintenance, and use restrictions must be identified on the
recording plan.
A.
A list of any approvals/permits relative to stormwater management
that will be required from other governmental agencies (e.g., a water
obstruction permit from PaDEP or approval from Allegheny County Planning),
and anticipated dates of submission/receipt should be included with
the preliminary plan submission. Copies of applications must be submitted
to the borough.
B.
A list of any permits relative to wetlands along with a wetlands
study must be submitted to the borough if wetlands are found on the
development site. The wetlands study must be prepared, signed and
sealed by a person certified to do such work.
The preliminary application shall contain a proposed maintenance
plan for all stormwater control facilities, in accordance with the
following:
A.
Identify the proposed ownership entity (e.g., municipality, property
owner, a homeowners, association, other management entity).
B.
If ownership is to be an entity other than the borough, include a
maintenance program for all facilities, outlining the type of maintenance
activities, probable frequencies, personnel and equipment requirements,
and estimated annual maintenance costs.
C.
Identify method of financing continuing operation and maintenance
if facility is to be owned by other than the borough or other governmental
agency.
